new-cert: create certificate files atomically.

2 files changed, 19 insertions, 9 deletions

diff --git a/Changelog b/Changelog
index 451eace..b23191f 100644
--- a/Changelog
+++ b/Changelog
@@ -2,6 +2,7 @@ lacme (0.3) upstream;
 
   + When parsing config-cert files and directories (default "lacme-certs.conf
     lacme-certs.conf.d"), import the default section of files read earlier.
+  + new-cert: create certificate files atomically.
   - Ensure lacme's config file descriptor is not passed to the accountd
     or webserver components.
   - new-cert: sort section names if not passed explicitely.
diff --git a/lacme b/lacme
index b654c7d..a8c25fe 100755
--- a/lacme
+++ b/lacme
@@ -524,16 +524,25 @@ sub spawn($@) {
 sub install_cert($$@) {
     my $filename = shift;
     my $x509 = shift;
-
-    open my $fh, '>', $filename or die "Can't open $filename: $!";
-    print $fh $x509;
-    foreach (@_) { # append the chain
-        open my $fh2, '<', $_ or die "Can't open $_: $!";
-        my $ca = do { local $/ = undef; $fh2->getline() };
-        print $fh $ca;
-        close $fh2 or die "Can't close: $!";
+    my @chain = @_;
+
+    my $tmp = "$filename.new";
+    open my $fh, '>', $tmp or die "Can't open $tmp: $!";
+    eval {
+        $fh->print($x509) or die "Can't print: $!";
+        foreach (@chain) { # append the chain
+            open my $fh2, '<', $_ or die "Can't open $_: $!";
+            my $ca = do { local $/ = undef; $fh2->getline() };
+            $fh2->close() or die "Can't close: $!";
+            $fh->print($ca) or die "Can't print: $!";
+        }
+        $fh->close() or die "Can't close: $!";
+    };
+    if ($@) {
+        unlink $tmp or warn "Can't unlink $tmp: $!";
+        die $@;
     }
-    close $fh or die "Can't close: $!";
+    rename($tmp, $filename) or die "Can't rename $tmp to $filename: $!";
 }